Track expected git errors in logs

Sometimes it is expected that a GitCommand executed in repo fails. In
such cases indicate in trace logs that the error was expected.

Bug: b/293344017
Change-Id: If137fae9ef9769258246f5b4494e070345db4a71
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/387714
Commit-Queue: Jason Chang <jasonnc@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Tested-by: Jason Chang <jasonnc@google.com>

git_command.py

@@ -286,6 +286,7 @@ class GitCommand(object):
         objdir=None,
         verify_command=False,
         add_event_log=True,
+        log_as_error=True,
     ):
         if project:
             if not cwd:
@@ -362,6 +363,7 @@ class GitCommand(object):
                         "ReturnCode": str(e.git_rc)
                         if e.git_rc is not None
                         else None,
+                        "IsError": log_as_error,
                     }
                 )
                 event_log.ErrorEvent(